Antimicrobial and antiquorum-sensing activity of Conocarpus lancifolius Engl. (Combretaceae)

Multidrug resistance to antimicrobial agents is a rapidly increasing problem. New strategies are required to reduce microbial resistance and pathogenicity. These include inhibiting microbial virulence factors, such as quorum-sensing (QS). In this study, the leaf and fruit extracts of Conocarpus lancifolius Engl. were investigated for their antimicrobial and QS inhibitory activities. The ethyl acetate extract of the leaf (EAL) recorded a remarkable inhibition of the Gram-negative bacteria; Escherichia coli and Klebsiella pneumonia (23 and 20 mm, respectively), using the agar well diffusion assay. Also, it showed the highest antifungal effect against Candida albicans (20 mm). Meanwhile, the ethyl acetate extract of the fruit (EAF) showed significant inhibition of the Gram-positive bacteria; Staphylococcus aureus and Bacillus cereus (20 and 21 mm, respectively). Measurement of the minimum inhibitory concentration (MIC) by the broth microdilution method indicated that Gram-positive bacteria were more susceptible to the antimicrobial effect of the investigated extracts. Particularly, EAL and EAF showed comparable activity to ampicillin against B. cereus (MIC, 312.5 µg/mL). The highest antifungal activity was recorded for the petroleum ether extract of the leaf (MIC, 625 µg/mL). Measurement of the inhibition diameter of pigment (PID) produced by the reporter strain, Chromobacterium violaceum indicated that EAL demonstrated higher QS inhibition (6 mm) compared to the standard, catechin (4.8 mm). In addition, the leaf and fruit extracts showed comparable activity to catechin (5 mm). The current study reported that C. lancifolius could be a promising antimicrobial and anti-quorum sensing drug candidate.